The world's demand for energy continues to grow due to population growth and improving standards of living. At the same time, the days of fossil fuel and gas are diminishing constantly. Although, the existing resources will be able to meet the global demand of fuel and chemicals for next two decades. Time has come to discover alternative resources for potential future fuel and more efficient up gradation of natural fuel resources. Globally, there are abundant supplies of natural gas, much of which can be developed at relatively low cost. The current mean projection of global remaining recoverable resource of natural gas is 16,200 Trillion cubic feet (Tcf), 150 times current annual global gas consumption, with low and high projections of 12,400 Tcf and 20, 800 Tcf, respectively. Natural gas is basically having a methane conc. of up to 85% alongside impurities such as sulphur and carbon dioxide as the chief impurities. Some time, it may contain sizeable amount of CO2 (upto 25%) as impurity. Hence, any transformation requiring direct conversion of natural gas must be having robust catalytic system with least possible time bound deactivation.
The up gradation of methane or natural gas to valuable chemical feedstock proceeds through indirect routs by initial conversion to syngas (a mixture of carbon monoxide and hydrogen). The production of syngas can be carried out by steam reforming (SR) (very large scale process) and even through partial oxidation of methane (PDX). Although partial oxidation of methane have high methane conversion with excellent syngas selectivity and extremely fast reaction kinetics, but is suffer from local heat generation over the catalyst and safety issues. Whereas the SR do not suffer from those safety issues but steam reforming of methane produce CO2 along with syngas which need to remove before its downstream GTL applications.
However, despite of unfavorable thermodynamics dry reforming of methane has some unique advantages; it can generate syngas at unite CO/H2 ratio, moreover it becomes advantageous because of the use of two greenhouse gases at a time. Low quality natural gas can be utilized for syngas production in near future; even the source gas does not need any further purification. A fundamental option currently explored is to reduce CO2 to chemicals and energy carriers using reduction equivalents from renewable resources. From this perspective the dry reforming of methane over metal based solid catalyst has drawn much attention in recent years and is now viewed as an area to produce ultra pure hydrogen or syngas for future fuel alternatives. As this would conceptually allow the efficient valuation of methane and the reforming technology requires the preparation of thermally stable and coke resistant CO2 reforming catalyst. The conventional supported nickel catalyst used for methane reforming are very active for carbon formation leads to rapid deactivation of catalyst, while coke-resistance alternatives (Rh, Ru, Pt etc) are bounded by its availability and high cost. So economic boundary conditions dictate the use of Ni based catalysts. There are reports on dry reforming of methane over different solid catalyst but to the best of our knowledge there is no reference for the use of gadolinium (Gd) promoted Ni-ZSM-5 catalyst for this purpose.
ZSM-5 (ZEOLITE SOCONY MOBIL-5) is an aluminosilicate zeolite belonging to the pentasil family of zeolites. Its chemical formula is NanAlnSi96-nO192.16H2O (0<n<27). Reference may be made to article in the Catalysis Today, 2011, 171, 132-139 by I. Sarusi et al. where they got about 19% methane conversion with CO/H2 ration of over doped Rh/Al2O3 catalyst.
Reference may be made to article in the Green Chemistry, 2007, 9, 577-581 by S. Williams and his group reported the use of O2 permeable ceramic membrane for the CO2 reforming of methane to syngas. On this article they described a very high concentration of feed gas (notably 80% feed concentration) to get 28% methane conversion. The meanwhile it is been observed that the membrane reactor which catalyses the reaction itself get deactivated (50%) after 14 h.
Reference may be made to US patent no US2007/0253886A by Abatzoglou and his group. Where they used active metal (mainly Ni) deposited on non-porous metallic and ceramic support; the catalyst shows very high methane conversion of 98% at 800° C. with CO/H2 ratio of 0.98. But the catalyst stability was limited up to 18 h time on stream.
Reference may be made to article in the Chem Cat Chem, 2011, 3, 593-606, in which Glaser et al and his group reported a highly stable and porous zirconia as support. With 5% Ni supported on ZrO2 they achieved 75% methane conversion at 750° C. with a comparatively slow GHSV of 7.2×104 ml h−1 g−1.
Reference may be made to article in the Chemical Communication, 2001, 415-416 in which Japanese worker Fujimoto and his group reported the production of syngas by pulse irradiation technique on a mixture of CH4 and CO2 at low temperature and atmospheric pressure. They achieved almost 42% methane conversion with H2/CO ratio of 1.5 with 1:1.5 CH4 to CO2 feed ratio at 180° C. while in presence of NiMgO catalyst the same technique gives almost 69% methane conversion while the H2/CO ration goes down to 0.86 with 1:1 CH4 to CO2 feed ratio.
Reference may also be made to article in the ACS Catalysis, 2012, 2, 1331-1342, which Chou et al. reported a mesoporous tri-metallic composite of NiO—CaO—Al2O3 in the dry reforming of methane. In this report they found 89% of methane conversion at 750° C. whereas the GHSV is 15000 ml g−1 h−1. But the H2/CO ratio is only able to rise up to 0.88 at 750° C.
Reference may be made to article in the Catalysis Communication, 2001, 2, 255-260, in which Aika et al reported the use Ru supported titania catalyst over dry reforming of methane. At industrial condition, at 0.1 MPa and 800° C. the catalyst shows a stable activity for 25 h time on stream with CO2 conversion of −46%.
The drawback of the processes reported so far is that although they exhibit sufficiently high conversions of methane for high selectivity of syngas of unit H2/CO ratio but the rapid formation of coke causes deactivation of reforming catalyst. To overcome the deactivation many researchers used novel metals such as Pt, Ru, Rh etc but the rising cost and relatively poor availability desiccates the use of those catalyst in industrial purpose. On this economic boundation, Ni based catalyst will be the holy grail for methane reforming in coming future. There is, therefore, an evident necessity for further improvements in the Ni based catalyst and process for the dry reforming of methane with carbon dioxide.